Thesis (PhD)--Stellenbosch University, 2016.ENGLISH ABSTRACT: Natural forests are important habitats for many species. In the KwaZulu-Natal Midlands of South Africa these forests naturally exist as small isolated forest patches within a grassland matrix. Recently, much of the extensive grassland matrix has been converted to exotic pine plantations. It remains unclear how this has affected the ecologically important forest arthropods. The overall aim of this study is to determine the state of arthropod diversity in natural forest patches within a timber production landscape, and how best to conserve this diversity. The specific objectives of this study are to: 1) determine the impact of natural forest interpatch distance and forest patch size on epigaeic arthropod diversity; 2) compare arthropod species richness, abundance and composition among natural forests, pine plantations and grasslands; 3) determine how each arthropod functional guild/taxon (detritivores, predators, herbivores, ants and mites) responds to pine plantations, natural forests and grassland, and assess whether exotic pine plantations are able to function as habitat extensions of natural forests compared to the natural reference of grassland.
Natural forest patches and surrounding habitats were sampled for epigaeic arthropods using pitfall traps, Berlese-Tullgren funnels, and active searches. Large and small patches had similar species richness, while assemblages differed significantly. Greater ant richness was recorded in patches with closer interpatch distances, while the opposite was observed for mites. Interaction between patch size and interpatch distance led to large-close patches supporting ant, beetle and spider composition that is different from small-close patches. Additionally, small-distant and small-close patches supported different beetle and ant composition. However, large-close and large-distant patches supported similar overall assemblages. Natural forests surrounded by grassland maintain arthropod diversity better than those surrounded by pines. There were greater differences in assemblages between natural forest-grassland boundaries than between natural forest-pine boundaries, indicating edge effects between pines and natural forests. Furthermore, grassland supported higher ant richness, while the greatest richness of mites and detritivores was in natural forests. Natural forests and their surrounding habitats varied in assemblages among functional guilds, although natural forests and pines were similar in mite, herbivore and predator assemblages. Interestingly, some grassland associated species were often found in adjacent natural forests. Many natural forests associated species were also present in the surrounding pines, yet pine blocks negatively influenced natural forest associated mite species. All pine associated species were able to occupy adjacent natural forests.
Small patches had higher arthropod diversity than expected, although large and close patches are of greatest conservation priority in this landscape. Nevertheless, effective maintenance of all forest patches must incorporate surrounding natural vegetation. Although pines had a negative impact on species richness, they were also important habitat for some forest species, even though this is associated with loss of grassland species. I show that pines are not true extensions of natural forests, as they do not support all natural forest arthropod species. This study highlights the important role that natural forests play in the conservation of native arthropod biodiversity in a production landscape, and by extension in maintaining ecosystem processes across this landscape.AFRIKAANSE OPSOMMING: Natuurlike woude is belangrike habitatte vir baie spesies. In die KwaZulu-Natal Middelande van Suid-Afrika bestaan hierdie woude natuurlik as klein geïsoleerde bos-kolle binne 'n grasveldmatriks. Onlangs is groot dele van die uitgebreide grasveldmatriks omgeskakel na eksotiese denneplantasies. Dit is steeds onduidelik hoe hierdie veranderings die ekologies belangrike geleedpotiges in woude affekteer. Die oorkoepelende doel van hierdie studie was om die toestand van diversiteit van geleedpotiges binne natuurlike bos-kolle in 'n hout-produksielandskap te bepaal en om vas te stel wat die beste manier is om hierdie diversiteit te bewaar. Die spesifieke doelwitte van hierdie studie was om 1) die impak van natuurlike bos inter-kol afstand en bos-kol grootte op grondbewonende geleedpotige-diversiteit te bepaal; 2) geleedpotige-spesiesrykheid, -hoeveelheid en -samestelling tussen natuurlike woude, denneplantasies en graslande te vergelyk; 3) vas te stel hoe elke geleedpotige funksionele-gilde/takson (detritivore, roofdiere, herbivore, miere en myte) op denneplantasies, natuurlike woude en grasslande reageer, en om te bepaal of eksotiese denneplantasies as habitat-uitbreidings van natuurlike woude kan funksioneer met die natuurlike graslande as verwysing.
Grondbewonende geleedpotiges vanaf natuurlike bos-kolle en omliggende habitatte is versamel deur gebruik te maak van putvalle, Berlese-Tullgren tregters, en aktiewe soektogte. Bos-kol grootte het nie spesiesrykheid beïnvloed nie, terwyl spesiessamestelling opmerklik verskil het tussen groot en klein bos-kolle. Hoër mierspesiesrykheid was aangeteken in kolle met naby inter-kol afstande, terwyl die teenoorgestelde waarneming gemaak is vir myte. Interaksie tussen kol grootte en inter-kol afstand het daartoe gelei dat groot en naby kolle mier-, kewer- en spinnekopsamestellings ondersteun het wat verskil van klein en naby kolle.. Klein-ver en klein-naby kolle het ook verskillende kewer- en miersamestellings ondersteun. Maar, indien alle takson in ag geneem word, het groot-naby en groot-ver bos-kolle soortgelyke samestellings ondersteun. Natuurlike woude wat omring word deur grasveld handhaaf geleedpotige-diversiteit beter as dié omring deur dennebome. Daar was groter verskille in samestellings tussen natuurlike bos-grasveld rande as tussen natuurlike bos-dennebome rande, wat ’n aanduiding is van rand-effekte tussen denne en natuurlike woude. Grasveld ondersteun hoër mierspesiesrykheid, terwyl die grootste rykheid van myte en detritivore in natuurlike woude gevind is. Natuurlike woude en hul omliggende habitatte het verskil in hul samestellings van funksionele gildes, alhoewel natuurlike woude en dennewoude soortgelyke myt-, herbivoor- en roofdiersamestellings gehad het. Interessant genoeg, sommige grasveld-verbonde spesies is dikwels in die omliggende natuurlike woude aangetref. Baie spesies wat in natuurlike woude voorkom was ook teenwoordig in die omliggende dennewoude, maar denneplantasies het ’n negatiewe invloed op natuurlike woud-verbonde mytspesies gehad. Alle denne-verbonde spesies was in staat om die omliggende natuurlike bos te bewoon.
Kleiner bos-kolle het hoër geleedpotige-diversiteit gehad as wat verwag was, alhoewel groot en naby bos-kolle van die hoogste bewaringsprioriteite in hierdie landskap is. Tog moet doeltreffende instandhouding van alle bos-kolle die omliggende natuurlike plantegroei ook inkorporeer. Alhoewel denneplantasies 'n negatiewe impak op spesierykheid gehad het, was hulle ook belangrike habitat vir sommige woudspesies; daar was egter ʼn gepaardgaande verlies in grasveldspesies. Ek wys dat dennebome nie ware uitbreidings van natuurlike woude is nie, aangesien hulle nie alle natuurlike bos geleedpotige-spesies ondersteun nie. Hierdie studie beklemtoon die belangrike rol wat natuurlike woude speel in die bewaring van inheemse geleedpotige-biodiversiteit in 'n produksielandskap en dus ook in die handhawing van ekosisteem-prosesse regoor hierdie landskap
